Nobody on domain can RDP

On our domain, nobody has the ability to RDP all of the sudden. Everything was working just fine yesterday until about mid afternoon. No notable changes were made around the time this started happening either. We brought online a terminal server a little less than a month ago but that has never thrown us any problems either.

Following is what I have done to troubleshoot so far:

1) Made sure RDP was enabled (less secure mode)
2) Firewalls are disabled and pass ICMP traffic
3) Users are specified in RDP settings to have access to machine
4) Group policy to allow users to access via rdp
5) Confirmed that local security policies allowed rdp
6) Made sure AD RDP members / groups look accurate

I have also noticed this warning in event viewer on our domain controller. It started happening around 2:00 PM yesterday and occurs every 1-5 minutes.

"Certificate for local system with Thumbprint c3 c1 5c b0 f9 bc 57 5a f8 06 ef ca 2c 65 60 d9 ce d9 18 42 is about to expire or already expired."




This happened very randomly so I feel like something may have changed and I did not see or know about it. We are running Windows server 2012 r2.

Thank you
RDPError.PNG